This invention relates to a metallizing gun for applying sprayed metal which has a melting point below 350.degree. C., which is liquified by an electric heating means provided in the metallizing gun and which is atomized into droplet form by means of pre-heated compressed air.
Special metal alloys, which have been developed for such metal spraying procedures, are commercially available under the name "Cerro alloys" (alloys of bismuth). This metal spraying technique is employed in particular in the manufacture of moulds. Similar to the galvanoplastic technique, it produces exact but thinwalled mould shells with a faithful reproduction of surface details which are frequently backfilled for subsequent use. The present invention relates to a metallizing gun designed to execute this process.
In a metallizing gun of this type, the metal must be liquified in a container belonging to the gun and then maintained at the correct temperature. Moreover, the air required to spray the metal must be preheated also.
In former practice two heating elements with separate thermostatic controls were employed. It is important to maintain the correct temperature. Overheating the metal alloy is detrimental as is an overheating of the heating elements themselves. Simple thermostats, however, normally do not shut off until after the predetermined temperature has been exceeded. This in turn means that the alloy is usually overheated briefly. The element which heats up the air does not operate satisfactorily due to its inherent inertia. It is still cold at the beginning of the metallizing process, for example, and at the conclusion of the process, when the stream of air terminates, it overheats.